Conventionally, in image forming apparatuses such as copiers and laser beam printers, a method, in which arts toner development, an unfixed toner image having been transferred or, an image support such as plain paper is subjected to contact heating fixing using a heat roller system, has been used in many cases.
However, in such a heat roller system, it takes long time to achieve the fixable temperature by healing and also a large amount of heating energy is required. From the viewpoint of shortening the time from power activation to copy start (the warning-up time) and of energy saving, recently, a heat film fixing system has become mainstream.
In a fixing device (fixing unit) of this heat film fixing system, a seamless fixing belt, in which a releasable layer of e.g., a fluorine resin is laminated on fee outer surface of a heat-resistant film of e.g., polyimide, is used.
However, in a fixing device of such a heat film fixing system, since a film is heated, for example, via a ceramic heater and then a toner image is fixed on the film surface, the thermal conductivity of the film becomes critical. However, when tire fixing belt film is allowed to be thinner to improve the thermal conductivity, mechanical strength tends to decrease and then it becomes difficult to realize high-speed rotation, whereby formation of a high quality image at high speed becomes problematic and also a problem such that the ceramic heater is liable to break is produced.
To solve such problems, recently, a fixing belt itself provided with a heat-producing body (hereinafter, referred to as a heat-producing fixing belt) has been investigated and then a method has been proposed in which power is supplied to this heat-producing body, whereby the fixing belt is directly heated to fix a toner image. In an image forming apparatus using such a heat-producing fixing belt, warming-up time is shortened and power consumption is further reduced compared to the heat film fixing system. Therefore, a heat fixing device has been investigated, since excellent energy saving and speeding up are exhibited.
There is known a fixing belt having a heat-producing belt of a three-dimensional network structural body in which a core material made of, for example, iron, SUS, copper, cobalt, nickel, chromium, aluminum, gold, platinum, silver, tin, or palladium is covered with a fluorine resin, polyimide resin, polyamide resin, or polyamideimide resin (refer to, for example, Patent Document 1).
A heat-producing fixing belt provided with a heat-producing layer incorporating a polyimide resin in which a carbon nanomaterial and filament metal fine particles are dispersed, an insulating layer, and a releasing layer is known (refer to, for example, Patent Document 2).
There is known a heat-producing fixing belt having an insulating layer incorporating a polyimide resin, a resistance heat-producing body layer in which in a matrix resin containing a polyimide resin, a carbon nanomaterial and filament metal fine particles are substantially uniformly present by dispersion and, a releasing layer, and an electrode layer (refer to, for example, Patent Document 3).